Catheter and a method for manufacturing a catheter

ABSTRACT

A balloon catheter comprising a catheter ( 3 ) and a balloon ( 7 ) located at a distal end ( 5 ) of the catheter ( 3 ). A plurality of measuring electrodes ( 12 ) formed on a primary substrate ( 17 ) extend around the catheter ( 3 ) within the balloon ( 7 ). The primary substrate ( 17 ) is formed by a portion of a flexible resilient membrane ( 25 ) which also forms a secondary substrate ( 19 ). The measuring electrodes ( 12 ) are formed on the primary substrate ( 17 ) by first electrically conductive tracks ( 27 ) and second electrically conductive tracks ( 28 ) which are electrically connected to the first electrically conductive tracks ( 27 ) are simultaneously formed on the secondary substrate ( 19 ). The membrane ( 25 ) is coiled to form a roll, and the primary substrate ( 17 ) is also coiled around the rolled secondary substrate ( 19 ). The coiled primary and secondary substrates ( 17,19 ) is urged through a second lumen ( 20 ) in the catheter ( 3 ) from the proximal end ( 4 ) thereof to a radial slot ( 21 ) in the catheter communicating with the second lumen ( 20 ). The primary substrate ( 17 ) is urged through the radial slot ( 20 ) and wrapped around and bonded to the catheter ( 3 ) to form the measuring electrodes ( 12 ) as band electrodes.

BACKGROUND OF THE INVENTION

The present invention relates to a catheter, and to a method formanufacturing a catheter, for example, a catheter with one or moreelectrodes or a heating element formed on a surface thereof. Theinvention also relates to an assembly for use in the manufacture of acatheter.

Catheters having one or more electrodes formed on a surface thereof or aheating element formed on a surface thereof are known. Such cathetersmay be plain catheters, or balloon catheters. Catheters which areprovided with electrodes formed on an outer surface thereof aretypically provided to facilitate measuring of a transversecross-sectional dimension or a volume of a vessel or lumen in which thecatheter is located in a human or animal body, such as a blood vessel, acavity of the heart, the stomach, the urethra, the oesophagus, theintestine, and other such vessels, lumens and organs. Alternatively, theelectrodes may be provided for facilitating ablating of tissue in avessel or lumen by passing an electric current or a high frequencysignal through the tissue from one electrode to another. Where suchcatheters are provided with a heating element, the heating element maybe used also for ablating tissue by heating.

In general, where such catheters, either balloon catheters or plaincatheters, are provided with electrodes for measuring a transversecross-sectional dimension or the volume of a vessel or lumen, theelectrodes typically are located at a distal end of the catheter inspaced apart relationship relative to each other, and typically, areformed by band electrodes extending around the catheter. The twooutermost electrodes are provided as stimulating electrodes to which astimulating electric current is applied, and the electrodes locatedbetween the outermost electrodes are sensing electrodes on which avoltage response signal is developed when the stimulating electriccurrent is applied to the stimulating electrodes, and the catheter islocated in the vessel with an electrically conductive medium present inthe vessel. The voltage response signals developed on the sensingelectrodes are indicative of an adjacent transverse cross-sectionaldimension of the vessel or lumen. Alternatively, when the catheter isprovided in the form of a balloon catheter, the electrodes are locatedon the catheter within the balloon, and the balloon is inflated with anelectrically conductive medium. The voltage response signals developedon the sensing electrodes in response to an electric current signalapplied to the stimulating electrodes are indicative of an adjacenttransverse cross-sectional dimension of the balloon. Such catheters, bethey plain catheters or balloon catheters, will be known to thoseskilled in the art.

Catheters which are provided for ablating tissue in a vessel, lumen ororgan of a human or animal body ablate the tissue by applying anelectric current through the tissue or subjecting the tissue to a highfrequency current signal. In general, such catheters are of similarconstruction to those for measuring a transverse cross-sectionaldimension or volume of a vessel or lumen. In the case of catheters whichare provided with a heating element, the heating element, in general, isprovided by an electrically resistive track which is formed towards thedistal end of the catheter. By passing an electric current through theelectrically resistive track, heat is generated.

In all such catheters, be they balloon catheters or plain catheters, orbe they of the type for measuring a transverse cross-sectional dimensionof a vessel or lumen, or for ablating tissue in a vessel or a lumen, areprovided with electrodes or a heating element or heating elements on anouter surface of the catheter. The electrodes or heating elements mustbe coupled to corresponding ones or pairs of mutually electricallyinsulated electrically conductive wires, which in general extend througha lumen of the catheter from the electrodes or heating elements to theproximal end of the catheter for coupling to suitable electronic controland analytical equipment.

The manufacture of such catheters, be they balloon catheters or plaincatheters, is quite a complex, tedious and time consuming task. Firstly,the electrodes or heating elements must be secured to the outer surfaceof the catheter, which is a tedious and time consuming task. Secondly,the electrically conductive wires which are to be coupled to theelectrodes or heating elements must first be passed through a lumen inthe catheter from the proximal end thereof, and urged through one ormore radially extending openings from the lumen adjacent the electrodesor heating elements. The wires must then be electrically connected byeither soldering or by an electrically conductive adhesive to thecorresponding electrodes or heating elements. This is also a tedious andtime consuming task, and there is also the risk of the wires beingcoupled to the incorrect ones of the electrodes or heating elements.

There is therefore a need for a method for manufacturing a catheterwhich addresses the problem of producing catheters known heretofore, beit a plain catheter or a balloon catheter.

The present invention is directed towards providing such a method, andthe invention is also directed towards providing a catheter and aballoon catheter. The invention is also directed towards an assembly foruse in the manufacture of a catheter.

SUMMARY OF THE INVENTION

According to the invention there is provided a method for manufacturinga catheter, the method comprising providing a primary substrate havingat least one first electrically conductive element located thereon on anelongated carrier means, locating the carrier means in a lumen of acatheter with the primary substrate extending from the carrier meansthrough a radial opening from the lumen with the at least one firstelectrically conductive element exposed exteriorly of the catheter.

Preferably, the primary substrate is secured on an outer surface of thecatheter. Advantageously, the primary substrate is secured on thecatheter adjacent the radial opening. Ideally, the primary substrate issecured to the outer surface of the catheter.

In one embodiment of the invention the primary substrate is secured tothe outer surface of the catheter by bonding. Preferably, the primarysubstrate is bonded to the outer surface of the catheter by an adhesive.

In one aspect of the invention the primary substrate extends at leastpartially around the catheter, and preferably, the at least one firstelectrically conductive element is configured on the primary substrateto extend with the primary substrate at least partially around thecatheter.

In another aspect of the invention the primary substrate extendscompletely around the catheter, and preferably, the at least one firstelectrically conductive element is configured on the primary substrateto extend with the primary substrate completely around the catheter.

In one embodiment of the invention the primary substrate is of aflexible material, and preferably, the at least one first electricallyconductive element is flexible, and flexes with the primary substrate.

In one aspect of the invention the primary substrate is of a resilientmaterial.

In another aspect of the invention the primary substrate ispre-tensioned to coil inwardly.

In a further aspect of the invention the primary substrate ispre-tensioned to wrap around the catheter.

Preferably, the primary substrate is located adjacent a distal end ofthe carrier means.

In one embodiment of the invention the carrier means is located in thelumen by urging the carrier means through the lumen until the primarysubstrate is located adjacent the radial opening, and the primarysubstrate is urged through the radial opening from the lumen.Preferably, the primary substrate is wrapped around the carrier meansprior to urging the carrier means into the lumen. Advantageously, thecarrier means is urged into the lumen with the primary substrate wrappedaround the carrier means.

In one aspect of the invention the primary substrate is unwound from thecarrier means as the primary substrate is being urged through the radialopening in the catheter. Preferably, the primary substrate is wrappedaround the catheter as it is being unwound from the carrier means.Advantageously, the primary substrate is unwound from the carrier meansby rotating the carrier means in the lumen.

In one embodiment of the invention the carrier means is urged into thelumen from a proximal end thereof.

In an alternative embodiment of the invention the carrier means islocated in the lumen by urging the carrier means into the lumen throughthe radial opening until the carrier means is located in the lumen withthe primary substrate extending from the carrier means through theradial opening from the lumen.

In one aspect of the invention the at least one first electricallyconductive element is formed by an electrically conductive track formedon the primary substrate. Preferably, the at least one firstelectrically conductive element is formed on the primary substrate byone of a printing process, a deposition process and an etching process.

In another aspect of the invention the primary substrate comprises amembrane, and preferably, the primary substrate is of an electricallyinsulating material.

In another aspect of the invention a plurality of first electricallyconductive elements are provided on the primary substrate. Preferably,the first electrically conductive elements are spaced apart and mutuallyelectrically insulated from each other.

In one embodiment of the invention the carrier means comprises at leastone second electrically conductive element electrically connected to acorresponding one of the at least one first electrically conductiveelement on the primary substrate.

In one aspect of the invention the carrier means comprises a secondarysubstrate, and the at least one second electrically conductive elementis formed by an electrically conductive track extending longitudinallyalong the secondary substrate. Preferably, the electrically conductivetrack of the at least one second electrically conductive element isformed on the secondary substrate by one of a printing process, adeposition process and an etching process.

In one aspect of the invention the secondary substrate is of a flexiblematerial.

In another aspect of the invention the secondary substrate is of aresilient material.

In a further aspect of the invention the secondary substrate comprisesan elongated substrate defining an elongated longitudinally extendingcentral axis.

In another aspect of the invention the secondary substrate is of aresilient material and is coiled about the central axis to form anelongated roll.

In a further aspect of the invention the secondary substrate ispre-tensioned to coil around the central axis.

In one embodiment of the invention the secondary substrate comprises amembrane. Preferably, the secondary substrate is of an electricallyinsulating material.

In one aspect of the invention the primary and secondary substrates areof similar material. Preferably, the primary and secondary substratesare integrally formed in one piece from the same sheet of material.Advantageously, the first and second electrically conductive elementsare simultaneously formed on the primary and secondary substrates.

In one embodiment of the invention a plurality of the secondelectrically conductive elements are provided on the secondarysubstrate, the second electrically conductive elements beingelectrically insulated from each other, and being electrically connectedto corresponding ones of the first electrically conductive elements.

In an alternative embodiment of the invention the at least one secondelectrically conductive element comprises at least one elongatedelectrically conductive wire. Preferably, the carrier means comprises aplurality of elongated electrically conductive wires formed into a loom,the electrically conductive wires being electrically connected to thecorresponding ones of the first electrically conductive elements on theprimary substrate. Advantageously, each electrically conductive wire ofthe carrier means is electrically connected to the corresponding firstelectrically conductive element by wire bonding.

In one aspect of the invention an electrical connector is locatedadjacent the proximal end of the carrier means, and each secondelectrically conductive element terminates in the electrical connector.

In another aspect of the invention the primary substrate is located onthe catheter adjacent the distal end thereof.

In one aspect of the invention each first electrically conductiveelement forms an electrode.

In another aspect of the invention each first electrically conductiveelement comprises an electrically resistive heating element.

The invention also provides an assembly for use in the manufacture of acatheter, the assembly comprising an elongated carrier means, and aprimary substrate having at least one first electrically conductiveelement located thereon, the primary substrate being provided on thecarrier means.

In one aspect of the invention the carrier means is adapted for locatingin an elongated lumen of a catheter with the primary substrate locatedadjacent a radial opening in the catheter which communicates with thelumen, and with the primary substrate extending through the radialopening with the at least one first electrically conductive elementexposed exteriorly of the catheter. Preferably, the primary substrate isadapted to be wrapped around the catheter.

Additionally the invention provides a catheter having an elongated lumenextending from a proximal end, and a radial opening which communicateswith the lumen, and comprising an assembly according to the invention,with the carrier means of the assembly extending through the lumen fromthe proximal end thereof, and with the primary substrate extendingthrough the radial opening with the at least one first electricallyconductive element exposed exteriorly of the catheter.

Further the invention provides a catheter having a lumen extending froma proximal end and a radial opening which communicates with the lumen,and comprising an elongated carrier means extending through the lumenfrom the proximal end thereof, and a primary substrate having at leastone first electrically conductive element located thereon, the primarysubstrate extending from the carrier means through the radial openingwith the at least one first electrically conductive element exposedexteriorly of the catheter.

In one embodiment of the invention the catheter is a balloon cathetercomprising a balloon located on the catheter, the first electricallyconductive elements being located on the catheter within the balloon.Preferably, the balloon is located on the catheter, with the catheterextending through the balloon, and defining with the balloon a hollowinterior region extending around the catheter. Advantageously, theballoon is located adjacent the distal end of the catheter.

In an alternative embodiment of the invention the catheter is a plaincatheter.

The advantages of the invention are many. Catheters produced by themethod according to the invention can be produced relatively quickly andeasily. The primary substrate with the first electrically conductiveelements thereon can be produced separately of the catheter, and caneither be produced integrally with the carrier means or attached to thecarrier means to provide the assembly, which is also according to theinvention. The assembly of the primary substrate with the firstelectrically conductive elements provided thereon and with the carriermeans either integrally formed with the primary substrate or attachedthereto can then be readily easily fed into and through the lumen of thecatheter until the primary substrate is located adjacent a radialopening in the catheter, at which stage the primary substrate can bereadily easily urged through the radial opening and attached to thecatheter with the first electrically conductive elements exposedexteriorly of the catheter. This significantly increases the ease andsimplicity with which a catheter can be produced.

By providing the carrier means in the form of a secondary substratehaving second electrically conductive elements formed thereon which areeither connected to or integrally formed with the first electricallyconductive elements provides a further advantage in that the assembly ofthe primary and secondary substrates can be produced separately of thecatheter, and there is no danger of the second electrically conductiveelements being incorrectly connected to the first electricallyconductive elements.

By providing the primary substrate of a resilient material, the primarysubstrate can be coiled around the carrier means, and when aligned withthe radial opening can be urged through the radial opening by rotatingthe carrier means in the lumen. The resilience in the primary substrateresults in the primary substrate winding itself around the outer surfaceof the catheter as it is being unwound from the carrier means and urgedthrough the radial opening. Providing the secondary substrate as aresilient material which is coiled to form a roll has the additionaladvantage that the carrier means is relatively strong in torsion, thusfacilitating rotating of the carrier means for urging the primarysubstrate outwardly through the radial opening.

The advantages of the catheter according to the invention and theadvantages of the assembly for use in the manufacture of a catheteraccording to the invention are substantially similar to the advantagesdiscussed above which are achieved by the method according to theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the followingdescription of a preferred embodiment thereof, which is given by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 is a side elevational view of a balloon catheter according to theinvention having been manufactured by a method also according to theinvention,

FIG. 2 is an enlarged transverse cross-sectional end elevational view ofa portion of the balloon catheter of FIG. 1 on the line II-II of FIG. 1,

FIG. 3 is a perspective view of a portion of the balloon catheter ofFIG. 1 being formed by the method according to the invention,

FIG. 4 is a side elevational view of an assembly also according to theinvention for use in the manufacture of the balloon catheter of FIG. 1,

FIG. 5 is an enlarged end view of the assembly of FIG. 4 from one end,

FIG. 6 is an enlarged cross-sectional end view of the assembly of FIG. 4on the line V-V of FIG. 4,

FIG. 7 is an enlarged developed plan view of the assembly of FIG. 4, and

FIG. 8 is a side elevational view of the assembly of FIG. 4 beingformed.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, there is illustrated a catheter according tothe invention, which in this embodiment of the invention is a ballooncatheter, indicated generally by the reference numeral 1. The ballooncatheter 1 comprises an elongated catheter 3 extending from a proximalend 4 to a distal end 5. An inflatable element comprising a balloon 7 islocated on the catheter 3 adjacent to but slightly spaced apart from thedistal end 5 with the catheter 3 extending through the balloon 7 todefine with the balloon 7 a hollow interior region 8, which extendsaround the catheter 3. A first lumen 9 extends through the catheter 3from the proximal end 4 to the distal end 5 for accommodating aninflating medium for inflating the balloon 7, see FIGS. 2 and 3. An endcap 10 secured to the distal end 5 of the catheter 3 sealably closes thefirst lumen 9 adjacent the distal end 5 of the catheter 3. A pluralityof radial ports 11 extending radially through the catheter 3 from thefirst lumen 9 accommodate the inflating medium from the first lumen 9into the hollow interior region 8 of the balloon 7 for inflatingthereof.

A plurality of longitudinally spaced apart and mutually electricallyinsulated first electrically conductive elements, namely, measuringelectrodes 12, which are provided in the form of band electrodes extendaround the catheter 3 within the balloon 7. The measuring electrodes 12are provided for facilitating measuring of the transversecross-sectional area and/or diameter of the balloon 7 adjacent theelectrodes 12, as well as for determining the volume of the balloon 7.The measuring electrodes 12 comprise two spaced apart outermoststimulating electrodes 14 and a plurality of spaced apart sensingelectrodes 15 which are located between and spaced apart from thestimulating electrodes 14. The sensing electrodes 15 each produce avoltage signal in response to a constant electric current being appliedto the stimulating electrodes 15 when the balloon 7 is inflated with anelectrically conductive medium, for example, a saline solution. Thevoltage response signal produced by each sensing electrode is indicativeof the transverse cross-sectional area of the balloon 7 adjacent thatsensing electrode 15. In this embodiment of the invention the balloon 7is assumed to be of circular transverse cross-section when inflated, andthus, the voltage response signals produced on the sensing electrodes 15are indicative of both the values of the transverse cross-sectional areaand the diameter of the balloon 7 adjacent the corresponding sensingelectrodes 15.

Such balloon catheters will be well known to those skilled in the art. Adescription of such balloon catheters is provided in PCT publishedApplication Specification No. WO 2009/001328.

The measuring electrodes 12 are formed on a primary substrate 17 of anassembly, which is also according to the invention and indicatedgenerally by the reference numeral 18, and as well as the primarysubstrate 17, the assembly 18 also comprises a carrier means, namely, anelongated secondary substrate 19 from which the primary substrate 17extends. The assembly 18 is located in a second lumen 20 of the catheter3 with the primary substrate 17 extending from the secondary substrate19 through a radial opening, which is located intermediate the proximalend 4 and the distal end 5 of the catheter 3, and which in this case isprovided by an elongated radial slot 21 extending radially through thecatheter 3 from the second lumen 20 adjacent the distal end 5 of thecatheter 3 within the balloon 7. The primary substrate 17 is wrappedaround an outer surface 22 of the catheter 3, and is secured thereto aswill be described below with the measuring electrodes 12 exposedexteriorly of the catheter 3 within the balloon 7. The second lumen 20extends through the catheter 3 from the proximal end 4 to the distal end5 thereof, and is sealably closed at the distal end 5 by the end cap 10.

In this embodiment of the invention the primary and secondary substrates17 and 19 are integrally formed and are cut out from one single sheet ofmaterial, namely, a flexible membrane 25 of electrically insulatingmaterial. The membrane 25 is of polyimide material, and is relativelythin, in this embodiment of the invention the membrane 25 is ofthickness of approximately 25 microns, although the membrane 25 may beof thickness up to 150 microns. The membrane 25 is also relativelyresilient. The measuring electrodes 12 are formed on the primarysubstrate 17 by first electrically conductive tracks 27 which are formedonto the primary substrate 17 by a deposition process, in this case bymetal sputtering. A plurality of spaced apart mutually electricallyinsulated second electrically conductive elements, which in thisembodiment of the invention are provided by second electricallyconductive tracks 28 are formed onto the secondary substrate 19 by adeposition process, which in this case is also by metal sputtering. Thenumber of second electrically conductive tracks 28 is similar to thenumber of first electrically conductive tracks 27, and the firstelectrically conductive tracks 27 are connected to respectivecorresponding ones of the second electrically conductive tracks 28. Twoof the second electrically conductive tracks 28 are connected to the twostimulating electrodes 14 for applying the constant electrical currentto the stimulating electrodes 14. The remainder of the secondelectrically conductive tracks 28 are connected to corresponding ones ofthe sensing electrodes 15 for conducting the voltage response signalsfrom the sensing electrodes 15. The second electrically conductivetracks 28 are formed on the secondary substrate 19 simultaneously withthe first electrically conductive tracks 27 on the primary substrate 17by the same metal sputtering process. The second electrically conductivetracks 28 terminate in a connecting means comprising an electricalconnector 30 which is secured to the secondary substrate 19 at aproximal end 31 thereof for connecting to electronic control andanalysing equipment (not shown). The electronic control and analysingequipment may be operated under the control of, for example, a personalcomputer for applying the constant current signal to the stimulatingelectrodes 14, and for reading the voltage response signals from therespective sensing electrodes 15, for in turn computing the transversecross-sectional area and/or diameter of the balloon 7 adjacent therespective sensing electrodes 15 and the volume of the balloon 7.

The assembly 18 is formed with the membrane 25 lying flat and planar asillustrated in FIG. 7. The first electrically conductive tracks 27 toform the measuring electrodes 12 and the second electrically conductivetracks 28, together with connecting tabs 32 of the electrical connector30 are simultaneously formed by printing onto the membrane 25 by themetal sputtering process through a mask onto the membrane 25. Since themembrane 25 is of an electrically insulating material, the firstelectrically conductive tracks 27 are mutually electrically insulatedfrom each other as are the secondary electrically conductive tracks 28and the connecting tabs 32 also mutually electrically insulated fromeach other. The second electrically conductive tracks 28 are coated withan electrically insulating coating up to the point where they join thefirst electrically conductive tracks 27 which form the measuringelectrodes 12.

After forming of the first and second electrically conductive tracks 27and 28 and the electrically conductive tabs 32 onto the membrane 25, thepart of the membrane 25 which forms the secondary substrate 19 is coiledaround a longitudinally extending central axis 34 to form the secondarysubstrate 19 into an elongated carrier 35 in the form of a roll. On thesecondary substrate 19 being formed into the carrier 35, the primarysubstrate 17 is coiled around the carrier 35, so that with the primarysubstrate 17 coiled around the carrier 35, the carrier 35 can be enteredinto and urged through the second lumen 20 of the catheter 3 from theproximal end until the primary substrate 17 is located adjacent theradial slot 21. Although in FIGS. 2, 5 and 6 the primary substrate 17and the secondary substrate 19 are illustrated as being loosely coiledfor the purpose of ease of illustration, the primary and secondarysubstrates 17 and 19 are tightly coiled as the carrier and the primarysubstrate 17 are being entered into the proximal end 4 of the secondlumen 9, and are being urged through the second lumen 9.

With the carrier 35 located in the second lumen 20 and the primarysubstrate 17 located adjacent the radial slot 21, the proximal end 31 ofthe carrier 35 is gripped and rotated in the second lumen 20 in adirection corresponding to the rotational direction in which thesecondary substrate 19 was rolled to form the carrier 35 until alongitudinally extending free edge 37 of the primary substrate 17 isaligned with the radial slot 21. The carrier 35 is then rotated in theopposite rotational direction in the second lumen 20 for unwinding theprimary substrate 17 from the carrier 35 and urging the primarysubstrate 17 through the radial slot 21 and around the outer surface 22of the catheter 3.

The inherent resilience of the membrane 25 is such that once the part ofthe membrane 25 which forms the secondary substrate 19 is coiled intothe roll, and the primary substrate 17 is coiled around the secondarysubstrate 19, the secondary substrate 19 is retained in the roll by theinherent resilience of the membrane 25. Similarly, the primary substrate17 is also retained wrapped around the carrier 35 by the inherentresilience of the membrane 25. Thus, when the portion of the membrane 25which forms the primary substrate 17 is being unwound and urged throughthe radial slot 20, the inherent resilience of the membrane urges theprimary substrate 17 to wrap itself around the catheter 3.

The primary substrate 17 is then secured to the outer surface 22 of thecatheter 3 by bonding with an adhesive 36 with the first electricallyconductive tracks 27 exposed to form the measuring electrodes 12 as bandelectrodes.

A distal portion 38 of the carrier 35 extends axially beyond the portionof the membrane 25 which forms the primary substrate 17 in order to forma stabilising element 39 for engaging the second lumen 20 distallybeyond the radial slot 21 for stabilising the carrier 35 in the secondlumen 20 to facilitate rotation of the carrier 35 in the second lumen19.

Thereafter the balloon 7 is sealably secured to the catheter 3 with theradial ports 11 and the measuring electrodes 12 located within theballoon 7.

The second lumen 20 is sealed adjacent the proximal end of the catheter3 with the proximal end 31 and the electrical connector 30 extendingtherefrom. A coupling element (not shown) is sealably secured to theproximal end 4 of the catheter 3 to communicate with the first lumen 9for connecting the first lumen 9 to an inflating medium source (notshown).

To manufacture the balloon catheter 1, the catheter 3 is formed,typically by extrusion with the first and second lumens 9 and 20extending longitudinally therethrough, and if required, further lumensmay be formed during the extrusion of the catheter 3. The radial ports11 are then formed by, for example, drilling through the catheter 3 intothe first lumen 9. The elongated radial slot 21 is formed in thecatheter 3 to communicate with the second lumen 20. The assembly 18which is formed as already described is then entered into the secondlumen 20 from the proximal end 4 of the catheter 3 with the stabilisingportion 39 forming the leading end of the carrier 35. The carrier 35 isurged through the second lumen 20 until the primary substrate 17 islocated adjacent the radial slot 21.

The carrier 35 is rotated in the second lumen 20 in the rotationaldirection in which the roll of the carrier 35 is formed until thelongitudinal free edge 37 of the primary substrate 17 is aligned withthe radial slot 21. The carrier 35 is then rotated in the reversedirection to unwind the primary substrate 17 from the carrier 35 and inturn to urge the primary substrate 17 through the radial slot 21, whichin turn wraps itself around the outer surface 22 of the catheter 3 withthe measuring electrodes 12 exposed exteriorly of the catheter 3. Theprimary substrate 17 is then bonded to the catheter 3 by the adhesive 36with the measuring electrodes 12 exposed.

The proximal end 4 of the second lumen 20 is sealed with the carrier 35sealably extending through the second lumen 20, and the distal ends 5 ofthe first and second lumens 9 and 20 are sealably closed by the end cap10. Additionally, if desired, the second lumen 20 may be sealed atrespective opposite ends of the radial slot 21.

The balloon 7 is then sealably secured to the catheter 3 adjacent thedistal end 5 with the radial ports 11 and the measuring electrodes 12located within the balloon 7.

If, instead of a balloon catheter, the catheter according to theinvention is to be produced as a plain catheter without a balloon andwith measuring electrodes formed as band or other electrodes adjacentthe distal end of the catheter, the catheter according to the inventioncan be readily produced as a plain catheter by merely omitting theballoon 7 from the catheter 3.

It is also envisaged that instead of urging the assembly 18 of thecarrier 35 and the primary substrate 17 with the measuring electrodes 12thereon into the second lumen 20 from the proximal end 4 of the catheter3 towards the distal end 5 of the catheter 3 until the primary substrate17 is adjacent the radial slot 21, the assembly 18 may alternatively beurged through the second lumen by urging the proximal end of the carrier35 into the second lumen 20 through the radial slot 21, and the carrier35 would be urged through the second lumen 20 towards the proximal end 4of the catheter 3 until the primary substrate 17 is located adjacent theradial slot 21. The portion of the primary substrate 17 adjacent thecarrier 35 would be urged through the radial slot 21 into the secondlumen 9, so that the primary substrate 17 would extend from the carrier35 located within the second lumen 20 through the radial slot 21. Theprimary substrate 17 would then be wrapped around the outer surface 22of the catheter 3, and would then be bonded to the outer surface 22 ofthe catheter 3 as already described.

It is envisaged that in cases where the assembly 18 is entered into thesecond lumen 20 through the radial slot 21, the electrical connector 30would be connected to the proximal end of the carrier 35 and to thesecond electrically conductive tracks 28 after the assembly 18 had beenurged through the second lumen 20 to the proximal end thereof.

While the catheter according to the invention has been described ascomprising a balloon catheter, the catheter may be provided in the formof any other type of catheter, whether it be a plain catheter or aballoon catheter. It is also envisaged that the first electricallyconductive tracks which form the measuring electrodes on the cathetermay be provided for purposes other than for measuring values of atransverse cross-sectional dimension of a vessel or lumen in which thecatheter is located. For example, it is envisaged that the firstelectrically conductive tracks may be provided for applying a current ora high frequency signal to tissue adjacent the first electricallyconductive tracks for ablating the tissue.

It is also envisaged that instead of providing the first electricallyConductive tracks as electrodes, one or more of the first electricallyconductive tracks may be provided in the form of an electrical resistivetrack to form one or more heating elements which may also be used forablating tissue. In cases where the first electrically conductive tracksare provided as heating elements as opposed to electrodes, it isenvisaged that each track would be coupled to a pair of the secondelectrically conductive tracks for providing a voltage across the firstelectrically conductive tracks.

Additionally, while the measuring electrodes have been described asbeing band electrodes, while it is desirable that the electrodes shouldextend completely around the catheter, it is not essential that theelectrodes should extend completely around the catheter. Indeed, incertain cases, the electrodes could be provided as relatively small dottype electrodes, half band electrodes, quarter band electrodes or of anyother suitable configuration extending only partly around the catheter.It is also envisaged that where the first electrically conductive tracksare provided in the form of electrically resistive heating elements, thefirst electrically conductive tracks may be provided in any suitableconfiguration, besides band configuration.

While the carrier means has been described as being provided by asecondary substrate in the form of a flexible resilient membranesuitable for facilitating forming the second electrically conductivetracks thereon by a metal sputtering process, it is envisaged thatinstead of the carrier means being provided as a flexible membrane, thecarrier means may be provided in the form of a rigid or a semi-rigidsubstrate on which the second electrically conductive tracks would beformed by any suitable process. The primary substrate would then besecured to the rigid or semi-rigid substrate, for example, by adhesivebonding or the like, and the first and second electrically conductivetracks would be appropriately electrically connected.

It is also envisaged that the resilient membrane may be pre-tensioned tocoil inwardly around and along the central axis to form the carrier inthe form of a tightly formed roll, and to retain the carrier in thetightly formed roll. The portion of the membrane which forms the primarysubstrate would also be pre-tensioned to coil inwardly around thecarrier, so that as the primary substrate is being unwound from thecarrier and urged through the radial slot, the pre-tensioning in theprimary substrate would inherently cause the primary substrate to coiltightly around the outer surface of the catheter, so that the primarysubstrate would be tightly secured to the catheter by its own inherentpre-tensioned resilience.

It is also envisaged that in certain cases, where the primary substrateis pre-tensioned to coil around the carrier, the pre-tensioning in theprimary substrate could be such that when the primary substrate is urgedoutwardly through the radial slot to wrap around the outer surface ofthe catheter 3, the pre-tensioning of the primary substrate could besufficient to retain the primary substrate securely attached to thecatheter and extending around the catheter, without the need to bond theprimary substrate to the outer surface of the catheter.

While the membrane which forms the primary and secondary substrates hasbeen described as being formed of a flexible and resilient membrane,while it is desirable it is not essential that the membrane be of aresilient material. It is also envisaged that where the secondarysubstrate which forms the carrier means is of a rigid or semi-rigidsubstrate material, the primary substrate could be formed by theresilient material which could be pre-tensioned to coil around thesecondary substrate.

It is also envisaged that the carrier means may be provided as a loomcomprising a plurality of mutually electrically insulated electricallyconductive wires. The primary substrate would then be suitably attachedto the loom, and the wires in the loom would be suitably electricallyconnected to corresponding ones of the measuring electrodes by asuitable electrical coupling means, for example, by soldering oradhesive bonding or other suitable wire bonding techniques.

It is also envisaged that where the carrier means is provided by a loomcomprising a plurality of mutually electrically insulated electricallyconductive wires, the primary substrate may be provided by a resilientor a resilient pre-tensioned membrane pre-tensioned to coil inwardlyaround the wire loom, so that when urged outwardly through the radialslot, the pre-tensioned resilient primary substrate would wrap aroundthe outer surface of the catheter and would be secured thereto by theinherent pre-tensioned resilience of the primary substrate.

While the primary substrate has been described as being coiled aroundthe catheter, in certain cases, it is envisaged that the primarysubstrate may merely extend through the slot and would be bonded to thecatheter adjacent the slot. In which case, the primary substrate wouldnot extend around the catheter, and in such a case, the firstelectrically conductive elements would form relatively short electrodesor electrically resistive heating elements.

While it is advantageous, it is not essential that the primary substrateshould extend completely around the catheter.

While the first and second electrically conductive tracks have beendescribed as being formed onto a membrane by a deposition process, suchas metal sputtering, it is envisaged that the first and secondelectrically conductive tracks could be printed onto the membrane. It isalso envisaged that in certain cases the first and second electricallyconductive tracks may be etched from an electrically conductive foilwhich would be laminated onto the membrane.

Additionally, while the membrane has been described as comprising asingle sheet of material, in certain cases, it is envisaged that themembrane may be formed from a compound sheet whereby a plurality oflaminates of similar or different materials would be laminated togetherby bonding or any other suitable laminating means to form the singlesheet. In such cases, it is envisaged that one of the layers of thecompound sheet may be an electrically conductive layer, which would beetched to form the first and second electrically conductive tracks, in asimilar manner as a printed circuit board is formed.

While the balloon catheter has been described as comprising a pluralityof sensing electrodes, it is envisaged that in certain cases one singlesensing electrode may be sufficient, depending on the size of theballoon, and the use to which the balloon catheter is being put. It isalso envisaged in certain cases that a single stimulating electrode maybe sufficient.

It is also envisaged that in certain cases a stiffening means, such asan elongated stiffening element, for example, a relatively stiff wire,may be provided for stiffening the carrier means, to assist urging thecarrier means through the lumen. In the embodiment of the inventionwhereby the carrier is formed by rolling a secondary substrate to form aroll, the stiffening element could be provided such that the secondarysubstrate would be wound around the stiffening element. Similarly, in anembodiment of the invention where the carrier is provided by a loom ofwires, it is envisaged that the stiffening element could extendlongitudinally, for example, centrally through the loom. The stiffeningelement could be located such that it could remain a permanent fixturein the catheter, or it could be removed subsequent to locating theassembly in the catheter with the primary substrate extending throughthe radial opening.

Balloon catheters and plain catheters according to the invention andmanufactured according to the method of the invention are suitable foruse in many medical and surgical applications, for example, determiningthe volume or transverse cross-sectional area and/or diameter of avessel, lumen or organ of the human or animal body, for example, a bloodvessel, a cavity of the heart, the stomach, the urethra, the oesophagus,the intestine and other such vessels, lumens and organs. Ballooncatheters and plain catheters according to the invention andmanufactured according to the method of the invention are also suitablefor ablating tissue in a vessel, lumen or organ in a human or animalbody.

The invention claimed is:
 1. A method for manufacturing a catheter, themethod comprising: providing a catheter with an elongated lumenextending through the catheter from a proximal end thereof, and a radialopening communicating with the lumen, providing a primary substratehaving at least one first electrically conductive element locatedthereon with the primary substrate extending from an elongated carriermeans, wrapping the primary substrate around the carrier means, urgingthe carrier means with the primary substrate wrapped around the carriermeans through the lumen of the catheter from the proximal end thereofuntil the primary substrate is located adjacent the radial opening,urging the primary substrate through the radial opening, and wrappingthe primary substrate around the catheter with the at least one firstelectrically conductive element exposed exteriorly of the catheter.
 2. Amethod as claimed in claim 1 in which the primary substrate is securedon an outer surface of the catheter.
 3. A method as claimed in claim 1in which the primary substrate comprises a resilient material, and ispre-tensioned to coil inwardly to wrap around the catheter.
 4. A methodas claimed in claim 1 in which the primary substrate is unwound from thecarrier means as the primary substrate is being urged through the radialopening in the catheter.
 5. A method as claimed in claim 1 in which theprimary substrate is located on the catheter adjacent the distal endthereof, and each first electrically conductive element forms one of anelectrode and an electrically resistive heating element.
 6. A method asclaimed in claim 1 in which the primary substrate is secured to theouter surface of the catheter by bonding.
 7. A method as claimed inclaim 1 in which the primary substrate and the at least one firstelectrically conductive element extends at least partially around thecatheter.
 8. A method as claimed in claim 1 in which the primarysubstrate is unwound from the carrier means by rotating the carriermeans in the lumen.
 9. A method as claimed in claim 1 in which the atleast one first electrically conductive element is formed by anelectrically conductive track formed on the primary substrate.
 10. Amethod as claimed in claim 1 in which the primary substrate comprises amembrane of an electrically insulating material.
 11. A method as claimedin claim 1 in which the carrier means comprises at least one secondelectrically conductive element electrically connected to acorresponding one of the at least one first electrically conductiveelement on the primary substrate.
 12. A method as claimed in claim 11 inwhich the carrier means comprises a secondary substrate, and the atleast one second electrically conductive element is formed by anelectrically conductive track extending longitudinally along thesecondary substrate.
 13. A method as claimed in claim 12 in which thesecondary substrate comprises a membrane of an electrically insulatingmaterial.
 14. A method as claimed in claim 12 in which the primary andsecondary substrates are of similar material, and are integrally formedin one piece from the same sheet of material.
 15. A method as claimed inclaim 12 in which a plurality of first electrically conductive elementsare provided on the primary substrate spaced apart and mutuallyelectrically insulated from each other, and a plurality of the secondelectrically conductive elements are provided on the secondary substratemutually electrically insulated from each other, the second electricallyconductive elements being electrically connected to corresponding onesof the first electrically conductive elements.
 16. A method as claimedin claim 12 in which the secondary substrate comprises an elongatedsubstrate of resilient material defining an elongated longitudinallyextending central axis, and being coiled about the central axis to forman elongated roll.
 17. A method as claimed in claim 16 in which thesecondary substrate is pre-tensioned to coil around the central axis.